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On the aid afforded by agency of Bees to in the fertilisation of papilionaceous flowers, & on the crossing of Kidney Beans.—

Last year you published a brief notice by me on this subject. I therein stated that Bees always alight on the left-wing pla petal of the Scarlet Kidney-bean, & in doing this depress it; which & this acts on the tubular & spiral keel-petal, which causes the pistil to protrude; on the pistil there are is a brush of hairs, & by the mere repeated movement of the keel-petal cause the hairs brush out the pollen beyond the anthers on to the stigmatic surface. This complex contrivance led me to suppose that other visits of Bees were necessary to the fertilisation of the flower; accordingly I enclosed some few flowers in bottles & some under gauze, & those which were not in any way moved did not set a single pod, whereas some of those which I moved in imitation of the Bees produced fine pods. But I then stated that the experiment was tried on much too small a scale to be trusted. I have this year tried it on a large scale. covered up between three & four feet in length of a row of of the Kidney Beans, just before the flowers opened, in a tall bag

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of very thin net: nothing in the appearance of the plants would lead me to suppose that this was in any way injurious to their fertilisation; & I think this conclusion may be trusted, for some few of the flowers which I moved in the same way as the Bees do, not produced pods quite as fine as could be anywhere found in the uncovered rows. The same theory we the case with the pods of marked flowers of the common Beans with under the same sort of net in a following experiment. The result was that the covered up brought plants had produced by Aug 13th only 35 pods & in no one case two pods on the same stalk; whereas the adjoining uncovered rows were crowded with clusters of pods. When the bea There were many flowers on still on the upper plants when uncovered, & it was curious to see in a few days afterwards, as soon as the Bees had access to them, what a number of pods were set.— hanging in clusters of three & four together were produced. On Augst 17th I again put on the net on a later crop, & I expected from the season not being then so favourable, that the result would have been more striking: but the case was otherwise. The covered plants now produced 97 pods borne on 74 stalks, showing that the

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same stalk often produced more than one pod. This time I kept an equal length of uncovered beans ungathered, & on this length there were 292 pods or exactly thrice as many as on the covered plants. Taking this number as the standard of comparison for the first experiment (which, however, is hardly fair, as my gardener thinks the second crop was more productive than the first). There were thus produced more than eight times as many pods were produced in the uncovered than on the covered rows. (a)

In the common Bean there is no such obvious relations between the structure of the flower & the visits of Bees; yet when these insects alight on the wing-petals they cause the rectangularly bent pistil & pollen to protrude through the slit in the keel-petal. I was led to try the effect of covering them up, from a statement in the Gardeners' Chronicle made several years ago, namely that when Bees bite holes through the calyx of the Bean flower in order to get more easily at the nectar, the crop is injured. This was attributed by the writer to injury of the german ovarium, which I am sure is incorrect. But I thought that it was very possible that the fertilisation would be less perfect, as soon as bees ceased to alight on the wing petals. I accordingly covered up, just as the a few hours before the flowers were opened, 17 plants moving a few flowers flowers to make sure that good pods would be formed under the net, as did happen & first rate were produced. These 17 plants as [illeg] show to ascertain that very fine pods, including the full average number of beans could be & were produced on the plants under the net.

These 17 plants produced 36 pods; but no less than

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(a) text

The Kidney Bean is largely frequented by the thrips thrips, & as I have with some other plants actually seen a thrips b which was dusted with pollen leave several granules on the stigma, of it is quite possible that the fertilisation of the covered up flowers might have been thus aided.)

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eight of them, though well formed, did not include a single bean. The 36 pods together contained only 40 Beans, &, if the empty pods be excluded, each produced on an average less than one & a half bean; whence on the other hand 17 uncovered plants, which from an adjoining row which were visited by the Bees produced 45 pods, all including beans, & one as & 135 in number or on an average exactly three beans to the each pod. So that the uncovered Beans were nearly thrice as fertile as the covered.

In an old number of the Gardeners' Chronicle an extract is given from a New Zealand p newspaper in which it is stated much surprise is expressed that the introduced Clover never seeded freely until the Hive-bee was introduced. (a) Accordingly I covered up about a yard square of the common white clover, growing thickly in turf; & then gathered an equal number of the five heads from under the same sort of net & from the covered and uncovered plant, which were growing al round, & which I had seen daily visited by many bees. I collected the seed into a small parcel, & as far as I could estimate, the uncovered plants produced were just ten times as much seed as the covered. Speaking loosely, the covered heads might have been said to have produced no seed.

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(a) This statement may be erroneous; at least, as I shall immediately show, it does not apply to the Canterbury settlement. But I was induced by it to cover up under the same open sort of net about a yard

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(Lathyrus grandiflorus is very rarely visited by bees in this country; & from experiments which I have tried on during the two last summers, & from experiments recorded in Loudon's magazine, I am convinced that moving the flowers favours their fertilisation, even in even the frequent cases in which [illeg] the young when the young pod falls off, as very often happens almost immediately.

By an odd coincidence Sir W. Macarthur, who did not know of my experiments, told me that he had found that in New South Wales the introduced Erythrina did not set its pods well without the flowers were moved. From the statement in regard to the clover in New Zealand, I wrote to Mr. Swale of Canterbury in New Zealand & asked him whether leguminous plants seeded there freely before the Hive Bee was introduced; & he in the most obliging manner has sent me copious details a long [illeg] list of plants of this order, which seeded abundantly for several years before bees were introduced. And as he states that there is no indigenous bee (perhaps this statement applies to Bees resembling Hive or Humble bees, for some other genera are known to inhabit New Zealand), the fact that these plants seeded freely at first appears quite fatal to my doctrine. But Mr. Swale

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adds, that he beli believes that three species of a wasp-like insect performed the part of Bees, before the introduction of the latter; unfortunately he does not expressly state that he has seen them sucking the flower. He further adds a remarkable statement, that there are two or three kinds of grasshoppers which habituall frequent flowers, & he says he has repeatedly watched them "release the stamens from the keel-petal." So that, extraordinary as the fact is, it would appear that grasshoppers, though having a mouth so differently constructed, in New Zealand have to a certain extent the habits of bees. Mr. Swale further adds, that the garden varieties of the Lupine seed less freely than any other leguminous plant in New Zealand, & he says, "I have for amusement during the summer released the stamens of the with a pin, & a pod of seed has always rewarded me for my trouble, & the adjoining flowers not so served have all proved blind."— The case of the Lupine in New Zealand may be accounted for by the fact, if I dare trust my memory, that in England visited by Humble bees & not by hive bees.

These several facts, & the foregoing experiments, seem to me These experiments seems to me rather curious; for who would have imagined, seeing that these papilionaceous flowers are hermaphrodite, have an abundant supply of pollen & are so which is mature before the flower opens, & that the

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as neatly closed flower itself is so neatly closed, would have imagined that insects that Bees played so important a part in their fertilisation. I can hardly doubt that in England, during a season when Bees were very scanty, if in any one district large crops of seed = closer were planted, that they would partly fail from the corollas not being sufficiently moved.)

So convinced was I from these facts & from others not here given that the visits of Bees were highly important to the fertilisation of Leguminous plants, that I asked Dr. Hooker to have some plants of this order in the stores at Kew which had never seeded artificially fertilised with their own pollen; though & he now writes to me that this was done in the case of & that it has not pods. I have hardly any doubt that the movement of the wing-petal of the corolla would have sufficed;

These little foregoing little experiments, however, were not tried in relation to the agency of insects in fertilising a plant with its own pollen. Andrew Knight many years ago propounded the doctrine that no plant self-fertilises itself for a perpetuity of generations. After pretty close investigation, I am strongly inclined to believe that this is a law of nature throughout the vegetable & animal

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kingdoms.— I am well aware that there are no several cases of difficulty. Amongst these cases,

The Leguminosæ with papilionaceous flowers have been advanced by Pallas & others as a case in which crossing could never naturally take place. But any plant habitually visited by insects in such a manner that their hairy body hairy bodies, to which pollen so readily adheres, come into contact with the stigma, could hardly fail occasionally to receive the pollen from another individual of the same species. In all Leguminosæ the insect Bees do brush past over the stigma and the possibility [illeg] of crossing can plant of crossing would be be very very strong in the case of any plant so much the stronger, if the agency of insects were necessary for the its self-fertilisation; for it would show that they it were was habitually visited by them.)

(a) Believing so consequently that Leguminous plants although for reasons quite unintelligible to me, the crossing does not certainly see to be curious, only two or three cases as far as I know bring a record

Whether any one of your readers could had any experience on the natural crossing of Beans, Peas &c.

One Two remarkable cases are on record in the case of the kidney Beans & common Beans.

Mr. Coe of Knowle near Fareham Hants, in the most obliging manner sent me some specimens, & wrote

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(From these considerations I was led to believe that papilionaceous plants must be occasionally crossed. Nevertheless I must confess that from all such the evidence which as I have been able to acquire, crossing do between varieties growing close together does not take place nearly so freely as I should have expected. As far as I am aware only three or four cases of such crosses are on [illeg] record. in regard to cultivated varieties. It is not by any means, I believe, a common practice with seed-raisers to keep the crops of these their Leguminous plants separate. Hence I was led last year in my short communication to the Chronicle to ask

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to me stating that on the head last summer he had planted four rows of the dwarf Negro dwarf Kidney bean, between some rows of the white & brown Dwarfs, & likewise & near some tall scarlet runners. Then he had saved for seed. The plants themselves he feel some presented believes presented nothing remarkable in foliage, height, flowers, in their pods; but the beans themselves presented an extraordinary mixture, as I can testify from the sample sent me, of all shades between light brown & black, & a few mottled with white; not one-fifth or so more of the beans, perhaps much less were pure negroes. Some few of the beans also, of in the rows of the white haricot were affected, but none of the brown dwarfs.

(Hence then we apparently have one of those the extraordinary instance fact cases, which has been described by Wiegmann with in the case of several leguminous plants, experimentised on most carefully by Gärtner in the case of the pea, & mentioned described a few years ago by Mr. Berkeley in the Chronicle, in which of the pollen of a distinct one variety having affected not only the embryo but the tunics of the seed produced borne by the pure mother (a)) of another breed variety

This year I sowed the sample sent me extraordinary mixture harvested by Mr. Coe in 1857 of from the apparently crossed negro beans, believed by him to be quite pure; & the produce as might have been expected was the most extraordinarily heterogeneous mixture which could can be

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I have said that apparently we have here a fact of this nature; for I must state that Mr Coe sent me a dozen of the pure negro-beans which produced in 1857 the extraordinary mixture; & I sowed the dozen this year this year, which though quite like each other in appearance, produced plant differing in colour of flower &c & beans of various tints: so that these beans though not affected in their outer likeness as seem to have been crossed in the the product of a cross previous year of 1856.

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conceived; each plant differing from the others in tallness, foliage, colour, & size of flower, time of ripening & flowering, size, shape, & colour of pods, & beans of every conceivable tint from black to pale brown, some dark purple & some slightly mottled, they differed also in & of various sizes & shapes. (a) Mr. Coe tried took tried the experiment more philosophically, & separated the his crossed negro-beans into 12 lots, according to their appearance tints or of colour ; & keeping a few of each as a sample, he sowed them & he has now harvested them separately. He has kindly sent me samples of all.

The variation is now much greater than it was in the parent-lot of 1857. Beans of new colours have appeared, such as pure white, bright purple, yellow, & many more are much mottled. Not one of the 12 lots has transmitted its own tint to all its the beans produced by it; nevertheless, when the dark beans have clearly produced a greater number of dark, & the light coloured beans a greater number of light beans colour. The mottling seems to have been strongly inherited, but always increased. To give one example of one case of the greatest variability, from a a dirty brown bean, nearly intermediate in tint between the darkest & lightest, produced a

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My gardener remarked, (& Mr Coe has made the same remark with as did Mr. Coe with respect to some of his plants that some of the seedlings seemed to have been crossed by the scarlet runner; one of my plants ran along trailed on the ground for a length of four feet, & its flowers were white & its pods were so very long flat & broad; the beans were pinkish purple in tint & twice as large as those of the negro; shot through the flowers were white, I think this must have been the case: the beans in this plant were fine light purple but in two pods cases: there were also brown & purple beans in two in the same pod in two cases. All this looks extremely like These facts certainly seem to indicate a cross from the scarlet runner; but as the kind is generally esteemed a distinct species, I feel very doubtful on this head; & we should remember that it is well established that Mongrels (& some hybrids) frequently, or even generally, are much more vigorous than either of their parents.)

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sample, which I have been enabled to divide into no less than a dozen different tints, namely from pure white, black, purple, yellow, & eight other tints intermediate forms by vari between brown, slate, yellow, purple, or black. It has been stated that a few of the white haricots in the rows adjoining the negroes were in 1857 slightly treated affected: Mr. Coe sowed some of others which were of a very pale brown or cream-coloured; & he has sent me a pod from produced this autumn, which pod included two beans of the above tint & one of a pale dirty purplish-brown.

Now it may be asked are we justified in attributing all these singular fact this extraordinary amount of variation to crossing, whether or not the crossing was all confined to the year 1857; or may not the case be one of simple variation? I think we must reject the latter alternative. For in the first place the negro bean is an old variety & is reputed to be very true; in the second place, I do not believe any case is on record of several rows a vast number of plants of the same variety of plant all sporting at the very same period; & I may state that Mr Coe has collected several quantities of seeds the heterogenous seeds in 1857. On the other

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hand, the negroes bean having been planted between rows of white & brown brown beans, together with the facts which I have given on the importance of insect agency in the fertilisation of the kidney-bean, showing, which as may be daily seen, how incessantly the flowers are visited by bees, strongly favours the idea theory theory of crossing. Moreover the remarkable extraordinary increase in variability in the second generation or that of the years is strikingly confirms this idea conclusion, for the extreme variability of in the offspring from mongrels has been observed by all who have attended to this subject.

As seed-raisers do not usually take any precautions in separating their crops of leguminous plants, it may be asked, how are we to account for the extraordinary amount of crossing in Mr. Coe's plants in 1857, when almost every plant in the four rows of the negro seems to have been affected. I may here add that in an old paper in the Journal of the Bath Society, there is an almost exactly parallel account of the crossing of the several varieties of the common Bean throughout a whole field. Insect agency is always at work; but as the movement of the corolla will generally tend merely merely to push the flower's

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own pollen, which is mature as soon as the flower is open, on to the stigmatic surface; & even if pollen is brought by the Bees from another flower, the chances are in favour of pollen from the same variety being brought, where a large stock is cultivated.

I can explain Mr. Coe's case & that in the Bath Journal only on one hypothesis, with which I am not perfectly made satisfied ; namely that from some cause the negro bean did not at Knowle in 1857 at the produce good pollen, or produce matured it later than usual. This is know has been shown by Gärtner sometimes to happen occur, & would explain with the aid of insect-agency these whole cases. Believing as I do that it is a law of nature that every organic being should occasionally be crossed by with a distinct individual of the same species, & seeing that there is provision in the structure of flower in legum papilionaceous plants flowers causes the plants own pollen to be pushed on to its own stigma, I am inclined to speculate a little further. It is, I think, well ascertained that very close interbreeding tends to produce sterility at least amongst animals. Moreover in plants it has been

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ascertained that the pollen male organs fail in fertility more readily sooner than the female organs, & as Gartner both from hybridity & from other causes, & Gärtner has shown that in bringing back & further that they resume their fertility slower, when a hybrid is repeatedly crossed in successive generations with either pure parent. May we not then suppose that with Leguminous plants after a long course of self-fertilisation that the pollen begins to fail, & then, not till then, the plants are eagerly ready to receive pollen from some other variety? May Can this be connected with the extreme apparently short duration duration & constant succession of new varieties amongst our peas, & as is stated to be the case in France on the Continent with Kidney Beans?

Hence These speculations may be valueless, but I venture earnestly to request any of your correspondents who may have noticed any analogous facts on sudden & large variation in their seed-crops of any leguminous plants (including sweet peas) or any facts on such plants having kept true for many consecutive generations, when grown near each other, to have the kindness to take the trouble to communicate them to me or to the Chronicle or to the following address.

Down, Bromley Kent. C. Darwin

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October 5 1857 original Paper

& in Annals & Mag of N. History

Paper & Science on Crossing of Kidney Beans

Published Nov 14./58 in Gardeners' Chronicle

[in another hand:] (9) Box G Letter reviews Aug 1899 IX